BizTalk BAM - manually editing BTT XPath to return just the First instance of a Message Payload property?

We have a preference for using TPE for BAM tracking since it can be deployed independently of our orchestrations.

However, at one point in our process, we need to track a message payload property which has a 1:N relationship with the Root XML Element of the message.

与往常一样,如果我们尝试跟踪此消息,则会记录以下XLANG消息:

AmbiguousXPathException - The result set for the XPath expression ... 
contains more than a single node

我们试图直接修改btt-xpath以仅选择此属性的第一个实例

我试过了

'XPath="//*[local-name()='Property' and namespace-uri()='{URI}' ...]/[1]'

但随后得到错误“表达式必须计算为节点集”

更简单

'//Property[1]' and '//Property[position() = 1]'

别犯错,但这也不能把我的财产拿出来。

最后,有人能解释btt文件中xpath和somxpath之间的区别吗?